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Emerging Wildlife Diseases

A general assessment of the surveillance of diseases among wild animals throughout the world has just been drawn up by a Working Group of the Office International des Epizooties (OIE), which met in Paris in October*. The Group’s report identified three categories of disease:

With regard to diseases specific to wild animals, there were numerous reports concerning the emergence (or persistence) of serious diseases.

Several of these diseases are caused by pathogens that are transmissible to humans, including: The Ebola virus, isolated among Philippines macaques and red colobus monkeys in Côte d'Ivoire. The howler monkeys of the island of Trinidad are falling prey to the yellow fever virus and could be vaccinated in order to protect tourists who approach them. In Sierra Leone the Lassa fever virus killed several people who had been contaminated by rats. E. coli O157 H7, the “killer” enterobacillus, has been found in the meat and faeces of the American black-tailed deer which, though not appearing to suffer from it themselves, have contaminated eleven people. The reservoir for the Ehrlichia bacteria would appear to be white-tailed deer. Humans can be fatally infected by bites from the black-legged tick or the lone star tick which live as parasites on these cervidae.Bovine tuberculosis is still prevalent among the wild animals of all continents. In the Kruger Park (South Africa) this disease, which formerly affected mainly buffalo, has spread to kudu antelope and lions. Baboons, which had fallen victim to the disease in previous years, have been affected by a fulminating form that has wiped out the infected groups.Salmonellosis has claimed many victims among American and European wildfowl (thousands of gulls and ducks have died of the disease in France), as well as among European hedgehogs.Botulism has also struck a severe blow to the waterfowl of America (14 000 deaths) and of Europe (16 000 deaths in the North Sea).Tularemia remains a constant threat to hares in Europe, Northern Asia and the United States of America. In Estonia, an outbreak was reported in humans, in which the disease manifests itself as serious general disorders which can fortunately be cured by antibiotic treatment.Other diseases not communicable to humans continue to rage among American deer (viral epizootic hemorrhagic disease), European hares (brown hare syndrome: several hundred deaths in France in the autumn of 1996), pigeons or doves (trichomoniasis: several thousand deaths in France and the United Kingdom) and European foxes and chamois (sarcoptic mange). Sarcoptic mange is also affecting the chimpanzees of Tanzania and gorillas in Uganda’s "Bwindi Impenetrable Forest National Park".

Several long-standing diseases were again notified in 1997:

Rinderpest, affecting buffalo, giraffe and antelope in the national parks of East Africa since 1994 has not spread as much as was feared, but the vaccination of domestic cattle living in the region appears to have reduced the spread of infection. Likewise, foot and mouth disease, previously reported among the impala antelope of South Africa’s Kruger Park, appears to be dying out spontaneously.Classical swine fever is still striking wild boar, especially in Germany, France and Italy. No direct link has been proven to exist between the very serious epidemic that recently occurred among European domestic pigs and the cases observed in boar, but virologists fear that this disease might become endemic among wild populations. The anthrax bacillus remains one of the most fearsome killers of African mammals of all sizes and feeding habits, including elephant, rhinoceros, zebra and antelope. Carnivores (e.g. cheetahs) which feed on sick animals fall prey to the disease in their turn.Aujeszky’s disease affects the boar of Europe and the United States of America, where it appears that the natural means of spread is venereal. Almost 30 % of boar are said to have been in contact with the virus in 10 States in the United States of America. The viruses responsible for this do not, however, seem to be the same as those isolated in domestic pigs.Brucellosis remains a worrying problem among bison and wapiti in the American States of Idaho, Montana and Wyoming. In the Yellowstone Park, 1 300 bison died of starvation during the winter of 1996-1997, and 1 079 had to be shot or slaughtered. Serological analyses revealed that half of them had been in contact with the bacteria.Viral hemorrhagic disease of rabbits, the virus which escaped during an experiment to test its ability to curb the rabbit population of Australia, was introduced into the island of New Zealand where it spread widely among the wild rabbit population. For rabbits it is an extremely virulent pathogen, but fortunately it is harmless to other animal species and to man.Rabies among foxes is being eradicated in Western Europe, thanks to prevention campaigns that have been conducted for the past ten years or more involving the distribution of bait containing an anti-rabies vaccine. The same technique appears to have halted a rabies epidemic among coyotes which had spread from Texas to the northern United States of America. However, the disease was reported among Australian bats, one of which is said to have fatally contaminated an inhabitant of Brisbane in October 1996. Once again Newcastle disease has been reported among the wildfowl population, in which the virus is being isolated with increasing frequency. After infecting Canadian cormorants the disease went on to hit those of the United States of America, and 1 600 dead birds were counted in California. Luckily the virus responsible for the disease does not appear to pose much of a threat to domestic fowl. Although mycoplasmal conjunctivitis in house finches has assumed worrying proportions since 1994, now having spread to over 33 States in the United States of America and three provinces of Canada, it does not appear to be communicated to domestic fowl.

Rare diseases include the following curiosities:

Trichinella-like infection of crocodiles, which was found in farmed crocodiles in Zimbabwe. Trichinella is an intracellular parasite causing general and muscular disorders. It could be communicable to humans who eat the flesh of animals infected by the parasite.Brucellosis in marine mammals appears to be much more widespread than was originally thought, and numerous cases of this disease have been reported in Europe and the United States of America. In three cases the cause of the disease has not yet been identified:mysterious eagle mortality which has been observed among several dozen bald eagles, as well as among American coots in the United States of America. These birds lose their ability to fly and die with nervous symptoms.mysterious hair loss syndrome which is characterised by bilateral symmetrical alopecia and severe emaciation among the American black-tailed deer and mule deer.

All of this data collected by the OIE is a valuable source of information not only for veterinarians responsible for animal health, but also for the medical services of all countries. Indeed, recent experience has shown that wild animals very often provide the best warning of emergent diseases that might threaten domestic livestock and man.

Paris, 13 November 1997

The OIE, the world organisation for animal health, was created in 1924 and has its headquarters in Paris. It brings together 147 countries. Its task is to inform and advise the Veterinary Services of its Member Countries in order to contribute to the eradication of the most dangerous animal diseases for animals and humans and to determine the health standards for international trade.

(1) The OIE Working Group on Wildlife Diseases is chaired by Dr M. Woodford (USA). The group’s other members include Doctors M. Artois (France), R.G. Bengis (South Africa), V.V. Berezin (Russia), T. Mörner (Sweden) and V.F. Nettles (USA). It remains in constant contact with a network of consultants from different regions of the world.